Silicone compound is an ideal material for making molds of fossils, life castings and other hard objects. Like liquid latex, it gives a light, flexible, highly reproducible form. It also has additional advantages - longer service life and resistance to chemicals and degradation. This is the recommended material for making durable molds from important samples. Silicone molds for gypsum can be made in less time than a latex mold if “fast” catalysts are used. The only drawback is that it is more expensive than latex, and not so elastic, which leads to tears and damage.
The composition of the silicone material
This material consists of silicone paste as a base and a platinum catalyst that accelerates hardening.
When creating forms using silicone compound transparent, red, yellow, white and other colors. The hardener may also have a different palette or be colorless.
After mixing the two components at room temperature, the silicone mass becomes solid and acquires a rubber-like appearance. The usual cure time for most is between 18-24 hours, but the solidification time can be significantly reduced by using high-speed catalysts.
Types of Silicone Compounds
The most common rubber compounds used to make molds are RTV, RTV-2, and HTV. In contrast to RTV rubbers (vulcanizing at room temperature), HTV silicone requires hardening of temperature conditions in excess of 100 ° C.
Among those who produce silicone compounds, everyone is trying to make many silicones and catalysts with different viscosity, color and other functions.
There are two main classes of RTV silicones.
1. Tin-catalyzed silicones.
2. Silicones on platinum catalysts.
Each of them has its advantages and disadvantages. Tin-catalyzed silicones are generally cheaper and easier to use. They have a low to medium viscosity, which is why they streamline the product well. In contrast, platinum is suppressed by many naturally occurring compounds, in particular sulfur, tin, amines, just made polyester, epoxy or urethane rubber products. Even after coating the product with acrylic varnish, the silicone compound for molds on platinum will not solidify when interacting with sulfur and tin-containing surfaces. This makes them unsuitable for many natural objects. Nevertheless, after hardening, they have the greatest chemical, microbiological and heat-resistant ability and, in general, remain flexible for many years. In contrast, tin-catalyzed silicones tend to become brittle after several years of use and begin to break down or break. For these reasons, silicones in the tin group are often used for low volume casting operations. And platinum is used for important work, especially in large volumes.
Storage time
Many silicones can be used successfully up to 5 years from the date of purchase if they are stored properly in airtight containers in a dry, cool place. Nevertheless, the catalysts lose their effectiveness quickly enough, even with proper storage they are best used throughout the year.
Where apply
Silicone compound RTV-2 is used for making copies of various figurines. As well as art products from polyester, epoxy resins, wax, gypsum, candles, toys and soap, etc.
Pentelast Silicone Compound is food-safe and safe. The advantage of this material is that it has high flexibility and does not damage the product when removed, such rubber molds can be used repeatedly. Given that this is food grade silicone on a platinum catalyst, it can be used to make silicone molds for gypsum, molds for cakes and muffins, pastries and other confectionery products.
Safety note
Silicone compound is a relatively safe, odorless product when used properly, however, catalysts and thickeners can be toxic to the eyes and skin, so these parts of the body must be protected.
Procedure for creating molds
The surface of the copied sample is cleaned and degreased. If necessary, wax grease, soap solution or petroleum jelly is used.
The material is thoroughly mixed, since a precipitate may form during storage.
A container is prepared in advance, in which the basis for the impression is placed. Such a container may be a plastic cup, bottle or box. It should have a relatively straight bottom and sides without cracks and holes.
In a clean container, the base with the hardener is diluted until a homogeneous mass is formed.
In order to estimate the amount of silicone required, you need to calculate the volume to be filled so that the product is completely covered. Another option - you can simply cover the surface of the product with holes and cavities, after hardening, pour another portion of silicone, in this case, silicone and money are saved. In order to uniformly coat a sample, it is advisable to pour or apply silicone in two or more batches. The second batch is applied over the hardened first, but still sticky. You can also use gauze or other reinforcing materials for embedding between the layers, which allows you to make a more durable form.
The catalysts are mixed in proportions depending on the type of silicone. Some of them use a 50:50 ratio of base to catalyst. You can mix mechanically or manually with a spoon or stick. You can not get carried away for a long time by this process for no more than 2 minutes, since a long process forms many air bubbles in the mixture. In order to know whether a homogeneous consistency is obtained, it is better to take a color hardener.
After mixing, the mass pours out as quickly as possible. The material hardens to a rubbery state within 24 hours. At temperatures below +23 ° C, the setting time will be longer.
What to consider
Air bubbles can be nullified if you first mix a small part of the mixture and, using a brush, cover it with a sample. Thus, not only the annihilation of the bubbles is achieved, but also the clarity of the shape of the shape. After applying a thin layer, leave the product alone at room temperature until the mixture is free of air and freezes. Then the remaining portions of the hardener are mixed with the base and applied in layers to the products until they are finished. Under laboratory conditions, this process is simpler, as it is done using machines that shake the filled mold and release air. In underground conditions, you can shake it by tapping on the surface yourself.
If the sample has no natural boundaries, in order to prevent silicone from spreading during pouring, it will be necessary to build a retaining wall around the sample. This can be done with any inert material such as wood planks, clapboard, cardboard, etc. It is possible to fasten and seal the walls with adhesive tape so that silicone does not leak through the cracks.
Attention! Certain types of silicone may slightly discolor some types of rocks from which the cast is made. Before work, it is proposed to check and conduct an experiment with an insignificant sample before using them on valuable objects.